---
title: Gateway Migration Guide
subtitle: Migrating to the router from @apollo/gateway
description: Learn how to migrate a federated graph from @apollo/gateway to the Apollo GraphOS Router or Apollo Router Core without any changes to your subgraphs.
---

Learn how to migrate a federated supergraph using the `@apollo/gateway` library to the GraphOS Router or Apollo Router Core and gain significant performance improvements while making zero changes to your subgraphs.

## What's different?

Whereas `@apollo/gateway` is an npm package, the router is packaged as a _static, standalone binary_. 

The router exposes the most common critical features via declarative configuration. You customize the router with a [YAML configuration file](/router/configuration/overview/#yaml-config-file) that takes effect at startup. Configurations can be modified and take effect without restart if you either start the router with the `--hot-reload` flag or set the `APOLLO_ROUTER_HOT_RELOAD` environment variable to `true`.

Although you _can_ download the Apollo Router Core source and use it as a library in a larger project and as the basis for a self-hosted GraphOS Router, you may not need to because the features that were implemented by custom code with `@apollo/gateway` may be standard, supported features of the router.

## Take inventory of your gateway configuration

The `@apollo/gateway` library is an extension to the [Apollo Server](/apollo-server/) library, and you need to consider your existing configuration of _both_ gateway and server libraries when moving to the router. For example, you might need to consider your customizations for the HTTP headers your subgraphs receive from client requests, or for passing specific headers _back_ to the client from specific subgraphs.

Because the router uses an entirely different configuration mechanism, you should make a checklist of your gateway's custom behaviors to make sure those behaviors all remain when your migration is complete.

Start by looking for configuration and customizations in these places:

* Environment variables
* Non-Apollo telemetry and instrumentation (e.g., OpenTelemetry or Datadog)
* Constructor options passed to `new ApolloGateway({ ... })`
* Constructor options passed to `new ApolloServer({ ... })`
* Specific `plugins` passed to `new ApolloServer({ plugins: [ ... ] })`
* Custom middleware (e.g., Express, Koa, Fastify)

The sections below provide more details on what to look for in each of these categories.

## Environment variables

Many Apollo tools use environment variables prefixed with `APOLLO_` to set certain values, such as an API key for communicating with GraphOS Studio.

Make sure to note any environment variables you set in your existing gateway's environment, _especially_ those prefixed with `APOLLO_`

The router supports the following environment variables used by `@apollo/gateway`:

* `APOLLO_KEY`
* `APOLLO_GRAPH_REF`

The router **renames** the following environment variables used by `@apollo/gateway`:

* [`APOLLO_SCHEMA_CONFIG_DELIVERY_ENDPOINT`](/federation/managed-federation/uplink/#environment-variable) → `APOLLO_UPLINK_ENDPOINTS`
    * This argument supports providing a comma-separated list of URLs.

## `ApolloGateway` constructor options

The number of options you currently provide to your `ApolloGateway` constructor varies depending on whether you're using [managed federation](/federation/managed-federation/overview/). If you _are_ using managed federation, you might even be providing _zero_ options to this constructor!

### `supergraphSdl`

The [`supergraphSdl` option](/apollo-server/using-federation/api/apollo-gateway/#supergraphsdl) is used in _non_-managed federation to provide a composed supergraph schema via a file or other string. Usually, that schema is composed using the [Rover CLI](/rover/commands/supergraphs/).

You can achieve this option's effect with the router in one of the following ways:

* [Move to managed federation](/federation/managed-federation/setup/) with your move to the router.
* Provide the `--supergraph` command-line argument to the router on startup:

    ```
    ./router --supergraph supergraph-schema.graphql
    ```

    The router watches this schema file and hot-reloads it whenever it changes.

### `serviceList` / `IntrospectAndCompose`

If you provide one of these constructor options, your gateway performs its _own_ supergraph schema composition on startup. The router doesn't support this in-process composition.

Instead, you need to perform composition using [managed federation](/federation/managed-federation/setup/) or the [Rover CLI](/rover/commands/supergraphs/). With either of these methods, the router can hot-reload its supergraph schema without restarting, and you avoid the possibility of a composition failure that results in downtime.

### `buildService`

The [`buildService` function](/apollo-server/using-federation/api/apollo-gateway/#buildservice) enables you to customize the HTTP requests that the gateway sends to your subgraphs.

Common use cases include:

* Overriding subgraph URLs at runtime
    * In the router, you can use the [`override_subgraph_urls` option](/router/configuration/overview#subgraph-routing-urls).
* Propagating headers to subgraphs via `RemoteGraphQLDataSource`
    * In the router, you can use the [`headers` option](/graphos/routing/header-propagation).

### `logger`

The [`logger` constructor option](/apollo-server/using-federation/api/apollo-gateway/#logger) enables you to specify a different logger for messages that are produced by the `ApolloGateway`. By default, it inherits from the `logger` used by your `ApolloServer` instance.  This option is also useful for changing logging verbosity.

In the router, logging is JSON-structured in production environments by default, and you can adjust the verbosity. More advanced logging can be enabled through the use of [plugins](#plugins).

For more information, see [Logging in the router](/router/configuration/telemetry/exporters/logging/overview).

## `ApolloServer` constructor options

The `ApolloServer` constructor supports a large variety of options, but for the purposes of moving to the router, we'll focus on the following:

- `context`
- `plugins`

For the full list of options, see [`ApolloServer` options](/apollo-server/api/apollo-server#options). If you're using other options, additional steps might be necessary to replicate the same behavior. Please open a discussion on our [GitHub repository](https://github.com/apollographql/router) so we can understand your needs and help you with a solution.

### `context`

This constructor option is an object that enables you to propagate information across the request lifecycle. Use cases include:

* Authentication information
* Header propagation

The router provides [similar functionality](/graphos/reference/router/rhai#requestcontext).

### `plugins`

This constructor option is an array of built-in or custom `plugins` that extend Apollo Server's functionality. If you provide `plugins` to your `ApolloServer` instance, take note of each plugin's functionality and add it to your migration checklist.

Before you attempt to replicate a plugin's functionality via a router [customization](#supported-customizations), check whether any router [configuration options](/router/configuration/overview/) provide that same functionality. For example, the router supports options for propagating HTTP headers to subgraphs and enabling OpenTelemetry instrumentation.

If one of your `@apollo/gateway` plugins _does_ require a corresponding router customization, we encourage you to describe your use case in the router repo's [GitHub discussions](https://github.com/apollographql/router/discussions/). It might represent core functionality that the router _should_ provide out of the box, and we can help discuss the design.

For less common use cases, we also want to help build an ecosystem of shared customizations for the router, enabling teams to more quickly add the functionality they need before native support is available.

#### Supported customizations

The router supports two types of customizations that hook into the request-handling pipeline:

* [Rhai scripts](/graphos/routing/customization/rhai/)
    * Rhai is a scripting language designed for use with Rust applications.
* [External coprocessing](/router/customizations/coprocessor/)

Examples for each are provided in their respective documentation, and in the [Router repo](https://github.com/apollographql/router/tree/main/examples).

## Kubernetes deployment

For migrating to the router deployed on Kubernetes, see some tips for [configuring your router deployment](/router/containerization/kubernetes/#configure-for-migration-from-gateway).

## Responses and errors

Apollo Gateway runs its core GraphQL server using Apollo Server and a user configured HTTP server. GraphOS Router is built as an all-in-one product with the GraphQL and HTTP server bundled together. With this change there may be some slight difference to the logic of HTTP status codes or GraphQL error extension codes.

Refer the full list of [router error codes](/router/errors) for any changes to your gateway implementation. If you need to customize the responses, refer to [router customizations](/router/customizations/overview).

## Reporting migration issues

If you encounter a migration issue that isn't resolved by this article, please search for existing [GitHub discussions](https://github.com/apollographql/router/discussions/) and start a new discussion if you don't find what you're looking for.

## Additional resources

You can use the Apollo Solutions [router proxy migration strategy repository](https://github.com/apollosolutions/router-node-proxy) to run both `@apollo/gateway` and Apollo Router and conditionally proxy traffic to the router for a gradual release.

<SolutionsNote />
